There is a reason that major cities often turn out to have large black populations, krellin. It's not like the millions upon millions of the black population are lying when they talk about being marginalized due to their race whether you see it firsthand or not. You didn't see the genocide in Serbia under Milosevic firsthand either but it sure as hell happened. That stuff does happen, and inner city living is a perfect example of it.
Republicans can win in a black city by offering solutions to racial conflict, offering more funding to the rundown places, and, most importantly in my mind, cleaning up (*with the help of the local community* - that's important) the "violent" neighborhoods, specifically by targeting the illicit heroin and crack trade as well as staffing more police for those areas. They can also help in the long term by assisting in raising the lower and higher education standards throughout the inner cities. Fixing that problem would be no easy task, but it would help crime rates improve and help many families get out of the ghetto life through education and find good employment opportunities like you and I have and will. It would require the Republicans to adjust, but that's the hole they've dug themselves into by ignoring the cities based on your logic (which, I concede, isn't "bad" logic because it holds up historically, but you can't just assume that black communities have some predisposition that prevents them from voting red).
I strongly believe that lower taxes - hell, 1% would be great - would assist. But, unfortunately, due to people like Reagan (and Bush and Obama et al) that pushed forward a plan of attack to combat the rising debt without even accounting for the inevitable backlash from the other side no matter how reasonable their proposal was, we don't have that option. It's just not on the table. Every penny that the government, both local and federal, can get, they'll be taking, even if there's a Ron Paul in office in DC.
I'm not sure what vengeance politics are or what you mean by that. You're simply pointing out the inherent flaw in two-party politics. People think differently, and since there is no one to pick up the moderate role, the only way to keep your party happy is to grow ever more extreme and alienate yourself from the "morons" on the other side instead of working with them to find a middle ground, the only democratic way of doing things with two parties in charge. (Obviously the undemocratic way would be to turn into Hitler, which, albeit a tad bit ugly ... just a tad ... it worked as long as nobody challenged it.)